Treatment of cellulosic materials to impart flame resistance thereto



I Aug. 20, 1957 RUOM A. J. ERBEL ET AL v TREATMENT OF CELLULOSIC MATERIALS TO IMPART FLAME RESISTANCE THERETO Filed May 26, 1955 INVENTORS. flr/hur J. Erbe/ Duane L. Kenaga A TTOR NE Y5 United States Patent TREATMENT OF CELLULOSIC MATERIALS TO IMPART FLAME RESISTANCE THERETO Arthur J. Erbel, Bay City, and Duane L. Kenaga, Midland, Mich., assignors to The Dow Chemical Company, Midland, Mich., a corporation of Delaware Application May 26, 1955, Serial No. 511,393

6 Claims. or. 117-136) This invention relates to the treatment of normally flammable cellulosic materials to render the same fire retardant. More particularly, it relates to the treatment of cellulosic materials such as wood, paper, and textiles made from cotton and regenerated cellulose with a water, fire, and weather resistant composition containing a bis- (Z-haloalkyl) alkenyl phosphonate.

Because of its ready availability, ease of fabrication, and other reasons, wood is still widely used in construction of bridges, trestles, wharves, mine shafts, and other structures. In many such applications, costly measures are required to prevent and to extinguish fires. The use of oil-soluble wood preservatives is necessary in many instances to prevent decay of the wood. Such preservatives frequently increase the susceptibility of the wood to combustion. It would be desirable if a material could be found that would be compatible with wood preservatives and would also render the wood fire retardant. Many solutions to the problem of raising the ignition temperature of wood have been presented. Some of those methods involve coating the wood surface with a fire retardant composition. However, in such a method, when the Wood is cut or trimmed, the freshly exposed surfaces are no longer protected and require a new treatment. Other methods use water-soluble inorganic salts impregnated into the wood. Those salts are incompatible with the common oil-soluble preservatives and, in addition, are easily leached out of the wood by standing water or by rain. Still other methods precipitate a water-insoluble resin within the fibrous structure of the wood. Such methods, however, affect the important structural properties of the wood.

There are many applications for cellulosic materials other than wood which also require a water and weather resistant, fire retardant treatment. Among such materials may be mentioned textiles made from cotton and from regenerated cellulose, and paper.

The provision of a means for rendering normally flammable cellulosic materials fire retardant is the principal object of this invention.

A further object is the provision of a treatment for cellulosic materials in which the agent used is insoluble in water, to render the treated product weather resistant.

A still further object is the provision of a fire retardant treatment for wood in which the treating agent is compatable with the common oil-soluble wood preservatives.

The above and related objects are accomplished by impregnating the cellulosic material with a bis(2-haloalkyl) alkenyl phosphonate, preferably in a volatile solvent. After impregnation, volatile solvents may be removed from the cellulosic material, leaving the phosphonate uniformly distributed therein. When the solvents are of 2,803,562 Patented Aug. 20, 1957 low volatility, such as those used with oil-soluble wood preservatives, they may be left in the material.

The bis(2-haloalkyl)alkenyl phosphonates which may be used in accordance with this invention are those in which the haloalkyl and alkenyl groups contain the same number of from 2 to 3 carbon atoms and in which the halogen is chlorine or bromine. As typical examples of such compounds may be mentioned bis(2-chloroethyl)- vinyl phosphonate, bis(2-bromoethyl)vinyl phosphonate, bis(2-bromopropyl)propenyl phosphonate, and bis(2- chloropropyl) propenyl phosphonate.

The compounds of this invention are easily prepared from known starting materials. As exemplary of a method by which they may be made the preparation of bis(2-chloropropyl)propenyl phosphonate will be described. Bis(2-chloropropyl) 2-chloropropane phosphonate was prepared by adding P013 to 1,2-propylene 0xide at 45 to 50 C. The resulting tris-(2-:chloropropyl)- phosphite was then heated to 150 C. to form bis(2- chloropropyl) Z-chloropropane phosphonate by rearrangement. Equimolar amounts of the bis(2-chloropropyl) 2-chloropropane phosphonate and triethylamine were heated under reflux for 8 hours. The theoretical weight of amine hydrochloride was removed by filtration and the filtrate distilled under reduced pressure. The product was bis(2-chloropropyl)propenyl phosphonate and boiled at l52 C. at 3 mm. pressure. The other compounds useful in this invention may be prepared in a similar manner using the corresponding starting materials.

The solvents used in the impregnation step should be capable of dissolving the phosphonates of this invention in the concentrations required and should be easily volatilized. As examples of suitable solvents may be mentioned orthodichlorobenzene, aromatic mineral spirits, and ethanol.

The amounts of the compounds which should be retained by the cellulosic material to provide the desired fire retardancy may be varied within wide limits. When using wood, amounts as low as 2 pounds of the phosphonate per cubic foot of wood give some fire retardancy. With most woods, this represents about 2 to 3 percent of the weight of the wood. It is preferred, however, to use from 3 to 6 pounds of the phosphonate per cubic foot of wood. When textiles or paper are to be impregnated, the preferred amount of the phosphonate is from 10 to 30 percent of the weight of the treated material, although fire retardancy may be noticed with lesser quantities of the order of 2 percent or more.

The impregnation of wood may be accomplished by any known process, such as the full cell pressure process, empty cell process, or by soaking. The type of process used will depend on the end use of the wood, the species and condition of the wood, and by other factors well known to persons skilled in the wood impregnation art. After treatment, the solvent may be removed by air seasoning the wood or by known solvent removal processes.

The impregnation may also be carried out in conjunction with a wood preservative treatment. In this instance the phosphonate is dissolved at 5 to 40 percent concentration in the oil such as a petroleum-creosote solution that is to be used as a wood preservative. The impregnation can then be carried out by the processes previously mentioned.

Textiles and paper may be rendered fire-retardant by 3 dipping and soaking the materials in the previously described solutions. After soaking, the materials may be dried in air or by other known methods. The compounds of this invention do not alter the feel or hand of textiles nor do they seriously impair the properties of textiles or paper.

The compounds which are useful in this invention are insoluble in water and therefore are not leached out of the cellulosic materials by rain or by normal periods of standing in water. The compounds are stable under normal atmospheric conditions.

Cellulosic materials treated with the compounds of this invention successfully prevent the propagation of flames when the source of ignition is removed, and there is no afterglow when the flames are extinguished.

The invention will be more apparent from the following illustrative exmaples.

EXAMPLE 1 Blocks of ponderosa pine sapwood /2 by /2 inch by 3 inches were treated with a 25 percent solution of the compounds of this invention and with tris-(2-ch1oroethyl) phosphate, a compound having known effectiveness as a fire retardant. The impregnation was accomplished using a modified full cell process which used atmospheric pressure instead of the superatmospheric pressure normally used. The impregnation was carried out so that varying amounts of the compound were retained. The wood blocks were then allowed to season in the air for one month to remove substantially all of the solvent. They were then tested according to the procedure described in ASTM test El60-50. In that test 24 blocks are piled in a wire crib and a calibrated Meker burner placed under the crib for 3 minutes. After removing the burner the flames are allowed to burn until they are self-extinguished. The blocks are then weighed and their loss in weight recorded. The results of this test are recorded in Table I.

EXAMPLE 2 Twelve inch squares of M inch birch face veneer were cut and treated with the compounds of this invention and with other fire retardant compounds dissolved in aromatic mineral spirits, including triphenyl phosphate and tetrabromobutane. The impregnation of the panels was accomplished by soaking in the solution for 2 minutes then allowing them to season in air for 24 hours to remove the aromatic mineral spirits.

The panels were then subjected to an inclined plane flame test. In that test, a 12 inch square panel of wood is placed on a Wire rack so as to be at 45 degrees to the horizontal. A small cup holding one milliliter of alcohol is placed A inch below the veneer. The alcohol is ignited and the flame allowed to impinge on the veneer. The effectiveness of the compounds as fire retardants for the veneer was rated according to an arbitrary scale which included the time for the flame to penetrate through the veneer, the amount of area charred, and the time for the flames to extinguish themselves. According to this rating means no combustion, 1 means the flames were self-extinguishing, 2 means the flames continued but with evident retardancy and 3 means flaming never ceased. The results of the above test are listed in Table II.

EXAMPLE 3 Southern pine sapwood stakes /4 inch by A1 inch by 18 inches were treated with bis(2-chloroethyl)vinyl phosphonate. triphenyl phosphate, and tricresyl phosphate. The compounds were dissolved at 10 percent concentration in a wood preservative consisting of percent of a heavy petroleum oil equivalent to a #5 fuel oil and percent of a medium residue coal tar creosote. The impregnation was carried out by a full cell pressure process to a retention of 15 to 25 pounds of the solution per cubic foot of wood. After treatment, the stakes were placed upright in a cup. One milliliter of alcohol was placed in the cup and ignited. The losses in weight of the stakes are listed in Table III.

As can be seen, the fire retardant compounds of this invention give far greater fire retardancy when combined with common wood preservatives than do either triphenyl phosphate or tricresyl phosphate.

EXAMPLE 4 Strips of canvas duck were dipped into a 25 percent solution of bis(2-chloroethyl)vinyl phosphonate in aromatic mineral spirits (Penola and the solvent volatilized. The strips were then exposed to the blue flame of a microburner for 10 seconds, and the burner removed. The time for the flames to extinguish and the weight loss of the fabric were determined. The results are listed in Table IV.

Table IV Retention, Flames Wt. loss, Fire Retardant Percent by out, percent,

wt. seconds Bis(2-chloroethyl)viny1 phosphonate. g Control (untreated) Burned 99. n

It can be seen that bis(2-chl0roethyl)vinyl phosphonate provides considerable fire retardancy to canvas duck.

We claim:

1. An article of manufacture comprising a normally flammable cellulosic material and a bis(2-haloalkyl)alkenyl phosphonate in which the alkyl and alkenyl groups have the same number of from 2 to 3 carbon atoms and in which the halogen is selected from the group consisting of chlorine and bromine.

2. An article of manufacture as claimed in claim 1, wherein the normally flammable cellulosic material is wood.

3. An article of manufacture as claimed in claim 1, wherein the phosphonate is bis(2-chloroethyl)vinyl phosphonate.

4. An article of manufacture as claimed in claim 1,

wherein the phosphonate is bis(2-bromoethyl)viny1 phosphonate.

5. An article of manufacture as claimed in claim 1,

wherein the phosphonate is bis(2-chloropropyl)propeny1 5 ,6

phosphonate.

phosphonate.

UNITED STATES PATENTS Ladd Mar. Coover et a1. Mar. Coover et a1. Apr. Van Winkle June Kenega et al Nov References Cited in the file of this patent 

1. AN ARTICLE OF MANUFACTURE COMPRISING A NORMALLY FLAMMABLE CELLULOSIC MATERIAL AND A BIS(2-HALOALKYL)AL KENYL PHOSPHONATE IN WHICH THE ALKYL AND ALKENYL GROUPS HAVE THE SAME NUMBER OF FROM 2 TO 3 CARBON ATOMS AND IN WHICH THE HALOGEN IS SELECTED FROM THE GROUP CONSISTING OF CHLORINE AND BROMINE. 